Merge a fix from mysql-5.5 to mysql-5.1:

revno 2995.37.209
revision id marko.makela@oracle.com-20110518120508-qhn7vz814vn77v5k
parent marko.makela@oracle.com-20110517121555-lmple24qzxqkzep4
timestamp: Wed 2011-05-18 15:05:08 +0300
message:
  Fix a bogus UNIV_SYNC_DEBUG failure in the fix of Bug #59641
  or Oracle Bug #11766513.

  trx_undo_free_prepared(): Do not acquire or release trx->rseg->mutex.
  This code is invoked in the single-threaded part of shutdown, therefore
  a mutex is not needed.

storage/innodb_plugin/trx/trx0undo.c

@@ -1986,8 +1986,6 @@ trx_undo_free_prepared(
 /*===================*/
 	trx_t*	trx)	/*!< in/out: PREPARED transaction */
 {
-	mutex_enter(&trx->rseg->mutex);
-
 	ut_ad(srv_shutdown_state == SRV_SHUTDOWN_EXIT_THREADS);
 
 	if (trx->update_undo) {
@@ -2002,6 +2000,5 @@ trx_undo_free_prepared(
 			       trx->insert_undo);
 		trx_undo_mem_free(trx->insert_undo);
 	}
-	mutex_exit(&trx->rseg->mutex);
 }
 #endif /* !UNIV_HOTBACKUP */